Compete with NOS for L‐arginine, reducing NO production.Upregulated ARG2 in diabetes linked to endothelial dysfunction and decreased penile vasodilation.ARG1 variants also associated with severity of diabetic vascular complications (e.g., retinopathy).Involvement of ERK‐arginase, ROCK2 and p38 MAPK pathways further impairs cavernosal relaxation. The gene discussed is NOS1; the disease is diabetes mellitus.